The present invention relates to a container for microwave heating applications. More particularly, it relates to a thermoformed plastic food container or tray designed to resist overt torsional deflection when lifted by a user.
A wide variety of packaged, pre-made food items are sold to consumers. One particularly popular product type is pre-made food products that are served hot, and thus require heating by the consumer. Well known examples include lasagna, cheese macaroni dishes, and vegetable casseroles, to name but a few. These food items are sold to consumers in either a frozen or un-frozen state. Regardless, the food item must be heated prior to serving, such as by a conventional oven, a microwave oven, or boiling water.
In response to consumer demands for product handling convenience, pre-made heatable food products are commonly packaged and sold in useable trays or containers. From the manufacturer""s standpoint, these containers are not only aesthetically pleasing, but also promote stacking of multiple items and thus compact shipping and display. Consumers, on the other hand, require that the container be amenable to use within a conventional or microwave oven such that following removal of any extraneous packing materials, the container (and contained food item) can be placed directly within an oven and then heated as required.
As with any other product, consumers also require that the cost of pre-made food products be as low as possible. So as to satisfy this overriding goal, manufacturers make every effort to optimize material and manufacturing costs, including the costs of the useable container. To this end, the heatable containers used as packaging for pre-made food items are typically thermoformed plastic, as this technique is relatively inexpensive, and promotes rapid mass production. Over time, a xe2x80x9cstandardxe2x80x9d thermoformed plastic container design for packaged, pre-made food items has been developed. The container has a bottom and a continuous sidewall extending upwardly from the bottom. To facilitate uniform plastic flow during formation, the sidewall defines a small flange or return at a top end thereof (i.e., opposite the base). To minimize material costs, the flange is quite small, normally less than 0.125 inch in radial extension. Further, for ease of manufacture, the flange either extends only radially (relative to the sidewall), or has a single, uniform radius (such as with a rolled lip design). In this regard, a downward extension of the flange relative to the sidewall is also quite small, normally less than 0.125 inch. Of course, the size and shape of the container may vary greatly, and other features, such as handles, may be added. However, the basic design described above is universally applied.
Thermoformed plastic containers are highly viable in that they do not overly deteriorate when subjected to heat or microwaves. Unfortunately, certain potential drawbacks have been identified. For example, following heating in a microwave, the plastic container becomes less rigid. When a consumer uses two hands to lift the container by opposing sides thereof, the reduction in rigidity is of little concern. That is to say, a center of gravity of the contained food item is approximately located between the user""s hands (i.e., the food item is substantially centered relative to the container), so that a force generated by a mass of the food item upon lifting thereof is uniformly dispersed along the container. An all too common practice, however, is for the consumer to lift the container with one hand, grasping the container at a corner or single point. With this approach, as the container is lifted, the center of gravity of the contained food item is offset from the support provided by the user""s single hand. The force generated by the mass of the food item imparts a torque on the container, focused on the location of the user""s hand. Because the now heated plastic is less rigid, the container will relatively easily deflect or bend at the user""s hand, potentially causing the food item to fall out of the container. This is obviously highly undesirable. Further, due to the limited size of the flange, it is normally hot (via heat transfer from the sidewall. A user inadvertently grasping the heat container at the flange may experience discomfort or even burns.
Consumers continue to demand pre-made, heatable food items packaged in useable containers. Unfortunately, the standard thermoformed plastic container design useful for these applications does not account for torsional forces often encountered during handling following heating. Therefore, a substantial need exists for a thermoformed plastic heating container configured to resist deflection or bending when subjected to an off-center lifting force, such as when a user lifts the container with a single hand.
One aspect of the present invention relates to a thermoformed plastic food container for use in microwave heating. The container includes a bottom, a sidewall and a flange. The sidewall extends upwardly from the bottom, terminating at a top end. The flange extends from the sidewall opposite the bottom and includes a rim section and a return section. The rim section extends radially outwardly from the top end of the sidewall, and is curved in transverse cross-section. With this configuration, the rim section defines a radius in transverse cross-section. Further, an outer surface of the rim section is configured to receive a sealing film. Additionally, the rim section defines, in top plan view, at least one side that is longitudinally curved, preferably forming a convex curve relative to a central axis of the container. The return section extends from the rim section opposite the top end. More particularly, the return section extends generally downwardly relative to the rim section. The compound curve configuration of the flange resists deflection in response to a lifting force imparted at a single point of the flange. Thus, during use whereby a food item is contained with the container and heated, the container will not overtly deflect when a user lifts the container with a single hand.
Another aspect of the present invention relates to a thermoformed plastic food container for use in microwave heating. The container includes a bottom, a sidewall and a flange. The sidewall extends from the bottom and terminates in a top end opposite the bottom. More particularly, the sidewall includes a base section and an intermediate section. The base section extends radially outwardly from the bottom, and is curved in transverse cross-section. The intermediate section extends upwardly form the base section, and is curved in longitudinal cross-section. Finally, the flange extends from the top end of the sidewall. With this configuration, the compound curve configuration of the sidewall resists deflection in response to a lifting force imparted at a single point on the flange. Thus, during use whereby a food item is contained with the container and heated, the container will not overtly deflect when a user lifts the container with a single hand.
Yet another aspect of the present invention relates to a thermoformed plastic food container for use in microwave heating. The container includes a bottom, a sidewall and a flange. The sidewall extends from the bottom and terminates in a top end opposite the bottom. More particularly, the sidewall includes a base section and an intermediate section. The base section extends radially outwardly from the bottom, and is curved in transverse cross-section. The intermediate section extends upwardly form the base section, and is curved in longitudinal cross-section. The flange extends from the sidewall opposite the bottom and includes a rim section and a return section. The rim section extends radially outwardly from the top end of the sidewall, and is curved in transverse cross-section. With this configuration, the rim section defines a radius in transverse cross-section. Further, an outer surface of the rim section is configured to receive a sealing film. Additionally, the rim section forms, in top plan view, a longitudinally curved side. The return section extends from the rim section opposite the top end. The compound curve configuration of the flange and the sidewall resists deflection in response to a lifting force imparted at a single point of the flange. Thus, during use whereby a food item is contained with the container and heated, the container will not overtly deflect when a user lifts the container with a single hand.